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EVOLUTION
Chapter 15
• Evolution - change over
time
• Theory – a well-supported
testable explanation of
phenomena in the natural
world
Charles Darwin
The variety of living things…
BIOLOGICAL DIVERSITY
Darwin found a huge variety of living
things, each well adapted to their
environment
Voyage of the Beagle 1831
Patterns of Diversity
• Visited Argentina and Australiasimilar grassland ecosystems
–those grasslands were inhabited
by very different animals.
Patterns of Diversity
• Darwin asked questions…
–Why no rabbits in Australia,
despite the presence of habitats
that seemed perfect for them?
– Why no kangaroos in England?
Living Organisms and Fossils
• Darwin collected the preserved
remains of ancient organisms,
fossils.
• Some of the fossils resembled
organisms that were still alive
today.
Living Organisms and Fossils
Others looked completely unlike any
creature he had ever seen.
• As Darwin studied fossils, new
questions arose.
–Why had so many of these species
disappeared?
–How were they related to living
species?
The Galapagos Islands
• The smallest, lowest islands were
hot, dry, and nearly barren-Hood
Island-sparse vegetation
• The higher islands had greater
rainfall and a different assortment of
plants and animals-Isabela- Island
had rich vegetation.
The Galapagos Islands
• The shape of a tortoise's
shell could be used to
identify which island a
particular tortoise
inhabited.
More Galapagos Animals
The Journey Home
• Darwin Observed that characteristics of
many plants and animals vary greatly
among the islands
• Hypothesis: Separate species may have
arose from an original ancestor
Ideas that shaped Darwin’s Thinking
• James Hutton:
• 1795 Theory of
Geological change
–Forces change
earth’s surface
–Changes are slow
–Earth much older
than thousands
of years
Ideas that Shaped Darwin’s Thinking
• Charles Lyell
• Geographical
features can be built
up/torn down
• Darwin thought if
earth changed over
time, what about
life?
Lamarck’s Theory of Evolution
• Tendency toward Perfection
(Giraffe necks)
• Use and Disuse
• Theory of Acquired Traits
(characteristics)
Population Growth
• Thomas MalthusEnglish economist
• If population grew…
–Insufficient living
space
–Food runs out
–Darwin applied theory
to animals and plants
Publication of
On the Origin of Species
• 1859 after 25 years of
study, thought, struggle
• It outlined his theories of
natural selection and
evolution over time
His Studies of Variation
• Darwin didn’t know about genes
• He DID observe traits being passed to
offspring
• He knew about Artificial Selection –
nature provides variation, humans
select variations they find useful
• Dogs, pigeons, crops, horses, cows
Natural Selection
• There is a struggle for existence…living
things need food, living space
• Some individuals are better adapted for
their environment
• Adaptation – any inherited characteristic
that increases an organism’s chance of
survival
SURVIVAL OF THE FITTEST
Can you think of any adaptations?
• Check out these examples of adaptations
Descent with Modification
• Darwin proposed that living things
changed over long periods of time because
of natural selection
• It implies that all living organisms are
related
• Living things evolved from a common
ancestor
• Common Descent
• Tree of Life links all living things
Evidence of Evolution
• Fossil Record
• Geographic Distribution of living
things
• Homologous structures
• Vestigial organs
• Similarities in embryology
Geographic Distribution of Living Things
• Darwin found different species of animals on
different continents
• He recalled similar environments and
sometimes similarities in different animals
• Homologous Structures have different mature
forms but develop from same embryonic
tissues
• Vestigial organs are traces of
homologous organs
• Ex. Legs in skinks
(p. 385)
Similarities in Embryology
Similar in early stages…common ancestry?